1. Field of the Invention
The present invention relates to a planar antenna apparatus that uses UWB (ultra-wide band) and a method for fabricating such an antenna apparatus.
2. Description of the Related Art
In recent years and continuing, much attention is being focused on UWB as a wireless communications technology enabling radar positioning and broadband communications, for example. In 2002, the U.S. Federal Communication Commission (FCC) approved usage of the UWB within a frequency band of 3.1-10.6 GHz.
The UWB is a wireless communications technology that involves transmitting pulse signals across a very wide frequency band. Therefore, an antenna used for UWB communication has to be capable of transmitting and receiving signals within a very wide frequency band.
It is noted that in “An Omnidirectional and Low-VSWR Antenna for the FCC-Approved UWB Frequency Band” by Takuya Taniguchi and Takehiko Kobayashi (The 2003 IECIE General Conference, B-1-133), an antenna adapted for use in the FCC-approved frequency band of 3.1-10.6 GHz is disclosed that comprises a ground plane and a feed element.
FIGS. 1A and 1B are diagrams showing examples of conventional antenna apparatuses. The antenna apparatus 10 shown in FIG. 1A includes a ground plane 11 and a feed element 12 having a circular cone shape that is arranged on the ground plane 11. The circular cone shape of the feed element 12 is arranged such that the side face forms an angle of θ degrees with respect to the axis of the cone. It is noted that desired antenna properties may be obtained by adjusting the angle θ.
The antenna 20 shown in FIG. 1B includes a ground plane 11 on which a conical part 22a and a spherical part 22b internally touching the conical part 22a are arranged, the conical part 22a and the spherical part 22b forming a tear-shaped feed element 22.
As is described above, a conventional broadband antenna apparatus is constructed by arranging a cone-shaped or tear-shaped feed element on a flat ground plane. The antenna apparatus constructed in such a manner is rather large so that techniques for miniaturizing and flattening the antenna apparatus are in demand.